The traditional technology for designing and manufacturing color image photosensitive chips (or devices) takes the use of either single-layer photosensitive pixel, or three-layer photosensitive pixel. For a photosensitive chip using the single-layer photosensitive pixel, in order to obtain color images, it must be coated with a filter in accordance with a certain pattern, such as Bayer Pattern or honeycomb pattern. For a photosensitive chip using the three-layer sensing pixel, there is no need to use color filter. Those conventional technologies for designing and manufacturing color image photosensitive chips (or devices) are still yet to be improved.
In the traditional single-layer color image photosensitive chip, two different kinds of patterns are mainly used for obtaining color signal. FIG. 1 is the first kind of color filter pattern, namely a CYMG pattern (also called composite color filter pattern), which consists of cyan, yellow, magenta and green color. FIG. 2 and FIGS. 3(a), 3(b) are several primary color (RGB) filter patterns ordered as a Bayer Pattern or Honeycomb Pattern, respectively. Both of these two patterns consist of red, green and blue color.
In the color photosensitive chip made of CYMG pattern, the photosensitive pixel array comprises many macro-pixels. Each macro-pixel is composed of four pixels, each being coated by C, Y, M, G color filter respectively. However, the display industry uses the three primary colors (i.e. RGB) pattern rather than CYMG pattern, thus it is necessary to transform a color matrix for C, Y, M or G color to a matrix for RGB so as to convert CYMG pattern into RGB pattern. Moreover, because each pixel point senses only one color (either cyan, or yellow, or magenta, or green), to sense RGB colors by each pixel, interpolation is needed to interpolate the missed colors from the adjacent pixel points. In the color photosensitive chip of Bayer Pattern (U.S. Pat. No. 3,971,065), the photosensitive pixel array comprises many macro-pixels, each comprising four pixels coated with only RGB colors. Bayer Pattern further requires that in every macro-pixel, two elements on one of the diagonals must sense green or a color corresponding to luminance of the image, whereas the other two colors sensed are red and blue, or colors corresponding to two other different spectra of visible light. Similarly, since each pixel point senses only one color (red, or green, or blue), interpolation is needed to interpolate the missed colors from the adjacent pixel points for obtaining the other two missed colors at each point. Bayer Pattern has four different orderings, each representing a specific arrangement of the RGB position. In a honeycomb pattern as shown in FIG. 3, a macro-pixel comprises only three pixels coated by RGB colors and arranged in a hexagonal honeycomb shape. In the honeycomb pattern, pixels sensing RGB colors are arranged uniformly and symmetrically; and exchanging the positions of two pixels still yields a honeycomb pattern.
As described above, there are three common issues in implementing the color filter formed by a composite color (CYMG) pattern, Bayer Pattern, or honeycomb pattern: firstly reducing sensitivity due to the existence of the color filtering film (compared with the monochrome photosensitive chip); secondly reducing effective spatial definition (or resolution) due to color interpolation, which in return causes the third one, color aliasing. Normally, the color aliasing may be solved by using low-pass filters. However, low-pass filters will reduce the image definition, thereby worsening the second issue.
In order to avoid the reduction of sensitivity caused by the color filter and to enhance the overall photosensitivity, U.S. Pat. No. 6,137,100 discloses a method of balancing the sensing response of RGB photosensitive pixels, which makes use of the characteristic of photodiodes that have different sensitivities for different colors. Particularly, a photodiode is more sensitive to green, secondly red, and then blue. Therefore, areas sensitive to blue are made biggest, then to red and smallest to green. The improvement on color sensitivity with this method is still limited. Moreover this method just emphasizes the RGB color pattern.
Color photosensitive devices generally sense the continuous spectrum corresponding to RGB color. There are also monochrome image photosensitive devices that are sensitive to the entire visible spectrum, or the infrared spectrum, or both of them. The sensitivity of such a kind of monochrome photosensitive device is generally 10 times more than that of the traditional color photosensitive device of Bayer pattern (under the same physical condition of production), but such a device cannot produce color.
In a patent application titled “Multi-spectrum photosensitive device and manufacturing method thereof” (PCT/CN2007/071262) applied by the present inventor earlier, a photosensitive chip using two-layer photosensitive pixels is provided. According to this new method, the spectrum of top layer and bottom layer are layered in orthogonal or complementary form, as shown in FIG. 4 and FIG. 5, so that at any pixel positions, photosensitive pixels on top layer and bottom layer can respectively sense orthogonal or complementary spectrum (either the visible spectrum, or the spectrum of visible light and infrared), thereby maximizing the use of incident light energy. This method can be implemented by either using color filters or not, and also considering the advantages of spatial resolution ratio, color reduction, and photosensitivity. However, this new method did not optimize the design of physical structure of top layer and bottom layer.
The traditional technology for designing and manufacturing color image photosensitive chip (or device) has another characteristic, that is, sensing at the front side or the back side of the chip normally (such as U.S. Pat. No. 4,388,532, U.S. Pat. No. 4,679,068, U.S. Pat. No. 5,244,817, U.S. Pat. No. 6,169,369, U.S. Pat. No. 6,429,036, and U.S. Pat. No. 7,265,397). The U.S. Pat. No. 5,134,274] and U.S. Pat. No. 6,191,404 are mentionable for providing a two-sided photosensitive chip (and system) which can sense at both front side and backside simultaneously. The term “front side” means the side facing to the light source on the base layer of the chip, accordingly, the term “front side sensing” means sensing by photosensitive pixels at the front side; whereas term “back side” means the side back to the light source on the base layer of the chip, accordingly, the term “back side sensing” means sensing by photosensitive pixels at the back side. The back side sensing requires that the base layer of the chip is thin enough and may be sealed specifically so that light can penetrate through the base layer and be sensed by photosensitive pixels. Such a two-sided photosensitive chip is enabled to receive light from front side and back side simultaneously, thus having the characteristic of integrating signals of two different light sources. However such a kind of two-sided photosensitive chip merely contains one layer of photosensitive pixels located on a certain side of the base layer of the chip. Consequently, when a user needs to obtain color (or multi-spectrum) sensing signal, or to receive two different views (or contents) on a photosensitive chip, this kind of single-layer photosensitive chip which is enabled to sense at two sides encounters difficulty. In addition, the single-layer photosensitive chip which is enabled to sense at two sides requires of light signals from two directions, obverse and reverse, which has corresponding relation on the geometrical space, that is to say it can merely be used for single view.
Therefore, those prior arts of photosensitive chips still have disadvantages. As for single-layer photosensitive chip, bottleneck occurs on the aspect of sensitivity, and the utilization efficiency of space and energy thereof is no better than that of the multi-layered. And as for multi-layer (double-layer or three-layer) photosensitive chip, the process is more complex and difficult. Another function which no prior arts of photosensitive chip have is that, they cannot sense the light corresponding to different views from two directions, obverse and reverse.
Thus, it is still necessary to improve the prior arts to find out a sensing device and a manufacturing method thereof, which may combine the advantages of the monochrome image sensing device and color image sensing device, and can sense light from two different directions simultaneously or asynchronously for further enhancing the performance of sensing chip and extending the functions of single chip.